Refrigeration appliance and method for operating a refrigeration appliance

Abstract

The invention relates to a refrigeration appliance (11) with a refrigeration circuit operated by means of a linear compressor (1, 1') and with a controller (10) which is configured to control a working frequency (fw) of a lifting body (23) of the line compressor (1, 1'), said lifting body being driven by means of at least one drive magnet (9) equipped with at least one drive coil (9A), the control being carried out such that starting from an initial work frequency (fw,init), a phase shift (∆φ) between an electric voltage (U~) applied to the linear compressor (1, 1') and an electric current (Imeas) flowing through the linear compressor (1, 1') is determined and the working frequency (fw) is reduced incrementally until a predefined target phase shift (∆φtarget), the value of which is noticeably smaller than the phase shift for the initial working frequency (fw,init), is at least approximately reached. The invention also relates to a method for operating a corresponding refrigeration appliance (11). The invention can be particularly advantageously applied to domestic refrigeration appliances.

Description

[0001] Cooling device and method for operating a cooling device

[0002] The invention relates to a refrigeration device with a refrigeration circuit operated by a linear compressor and with a control or regulation system configured to regulate the operating frequency of a piston or cylinder of the linear compressor. The invention also relates to a method for operating a refrigeration device equipped with a refrigeration circuit operated by a linear compressor, in which the operating frequency of a piston or cylinder of the linear compressor is regulated. The invention is particularly advantageously applicable to household refrigeration devices.

[0003] Cooling devices are known whose refrigeration circuit uses a linear compressor as the drive. To achieve low energy consumption, the operating frequency of the piston is adjusted so that a predetermined resonance frequency of the oscillating system is matched as accurately as possible. The linear compressor is thus operated at a constant, predetermined operating frequency. Implementing this method in production requires that every linear compressor of the same type exhibit the predetermined resonance frequency as accurately as possible, which poses a major challenge for production and assembly because tolerances must be maintained within strict limits. Furthermore, the resonance frequency can change depending on load and temperature.Consequently, it often happens that the actual resonance frequency deviates from the predetermined resonance frequency, resulting in increased energy losses during operation of the linear compressor.

[0004] It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide a simple, reliable and energy-saving way of operating a linear compressor of a refrigeration device.

[0005] This object is achieved according to the features of the independent claims. Preferred embodiments can be found in particular in the dependent claims. The object is achieved by a refrigeration device with a refrigeration circuit operated by a linear compressor and with a control system configured to compensate for vibration orTo regulate the working frequency of a piston or cylinder driven by at least one electromagnet with at least one coil ("drive coil") as the lifting body of the linear compressor in such a way that, starting from an initial working frequency, a phase shift between an electrical voltage applied to the linear compressor and an electrical current flowing through the linear compressor is determined and the working frequency is gradually reduced until a predetermined target phase shift, which is noticeably smaller in magnitude than the phase shift at the initial working frequency, is at least approximately reached.

[0006] This method offers the advantage that the operating frequency can be automatically adjusted to the actual resonance frequency of, or close to, the actual resonance frequency of the reciprocating body or the associated vibration system, thus minimizing the power consumption of the linear compressor. This avoids the aforementioned problems of the prior art during compressor operation. In particular, a change in the actual resonance frequency of the reciprocating body or the associated vibration system due to changing boundary conditions such as temperature or load can be easily taken into account.

[0007] For example, in addition to the linear compressor, the refrigeration circuit may comprise at least one evaporator, at least one expansion medium and at least one condenser in a basically known manner.

[0008] The invention relates both to a linear motor in which the piston is driven as a lifting body and moves relative to the cylinder as a stationary component, and to a linear motor in which the cylinder is driven as a lifting body and moves relative to the piston as a stationary component.

[0009] The piston is arranged in a cylinder in a housing of the linear compressor. The piston and cylinder are mounted so that they can be moved longitudinally relative to one another, with one of the two being immobile in the cooling unit and relative to a coil of the motor, and the other being movable as a lifting body. The lifting body is articulated relative to the immobile component by at least one elastic spring element. The lifting body, which is equipped with at least one permanent magnet, is typically driven by the magnetic field of at least one drive magnet supplied with an alternating electrical voltage, thereby causing it to oscillate. Depending on the direction of movement, a working volume defined by the cylinder and an end face of the piston is increased or decreased. If the working volume is increased, refrigerant or working medium is sucked into the working volume at an inlet from a refrigeration circuit connected to the working volume.If the working volume is then reduced again, the working fluid is forced into the refrigeration circuit at an outlet. The amplitude of the alternating voltage determines the stroke of the reciprocating body, which in turn determines the mass flow of the working fluid in the refrigeration circuit. In the steady state, the working or oscillation frequency of the reciprocating body is determined by the voltage frequency of the alternating voltage signal. The efficiency of the linear compressor depends on the voltage frequency and thus the working frequency. The basic operation of a linear compressor in a refrigeration circuit of a refrigeration appliance is well known and will therefore not be discussed further here. The linear compressor can also be viewed as a linear motor, whose reciprocating body corresponds to the rotor or "mover."

[0010] The fact that the vibration or working frequency of the lifting body is controlled is based on the fact that the working frequency is not set to a predetermined, pre-calculated value, but is automatically set or adjusted using at least one feedback variable.

[0011] The phase shift is, in particular, smaller than zero because the current follows the voltage. The initial operating frequency is expediently chosen such that its distance from the (target) operating frequency at which the target phase shift is at least approximately to be expected is large, in particular so large that its phase shift allows a gradual approximation to the operating frequency at the target phase shift under all practically occurring operating conditions of the linear compressor. The initial operating frequency can, for example, be determined experimentally. The fact that the target phase shift is noticeably smaller in magnitude than the initial phase shift takes into account the effect that the phase shift remains essentially constant at a considerable distance from the resonance frequency (e.g., at approximately -90°), but drops in magnitude from this level in a comparatively narrow range around the resonance frequency (i.e., to values ​​> -90°).The fact that the specified target phase shift is noticeably smaller in magnitude than the phase shift at the initial operating frequency can mean in particular that the corresponding (target) operating frequency corresponds to the resonance frequency or is close to the resonance frequency.

[0012] The initial operating frequency is therefore above the resonance frequency. In contrast to an approximation from lower operating frequencies, this has the advantage that at high operating frequencies the stroke of the lifting body is small even at very high voltage (current) amplitudes. This is advantageous for a safe start if the control system does not initially know the current position or deflection of the lifting body. The second advantage lies in the phase shift between voltage and current, which at high initial operating frequencies has a value of approximately -90° or a magnitude of |-90°| = 90°. If the operating frequency is then reduced, it initially drops rather slowly, then drops significantly near or at resonance. In particular, the gradient is maximum at the resonance point. In this way, it can be reliably assumed that the operating frequency is in the resonance range.In contrast, if low operating frequencies are assumed, at least two extreme values ​​of the slope must be passed through before resonance is reached. Approaching from an initial operating frequency above the resonance frequency is therefore a particularly reliable and simple way to identify the resonance point.

[0013] The phase shift can therefore be understood as the phase shift as such or a value derived from it, such as the slope of the phase shift.

[0014] The operating frequency can be shifted with a constant or variable step size. For example, if the phase shift in an i-th step is still above the target phase shift and in an (i+1)-th step the phase shift is already below the target phase shift, the operating frequency can be set to the step whose phase shift is closest to the target phase shift. However, it is also possible that the target phase shift is achieved almost exactly.

[0015] In one embodiment, the operating frequency is reduced with a constant first step size Af > 0 until the specified target phase shift is approximately reached, and then the operating frequency is shifted with a constant smaller second step size Af' with Af > Af' > 0 (e.g. with Af' = Af / 2, Af / 5 or Af / 10) until the specified target phase shift is at least approximately reached. This advantageously achieves a particularly good approximation to the specified target phase shift. The shift with the smaller step size Af' can be carried out in both directions (i.e., to higher or lower frequencies). This exploits the fact that the phase shift Acp, starting from higher frequencies with Acp approx. -90° in the range between approx. -90° < Acp < approx. 0°, continuously decreases in magnitude or continuously increases in a sign-sensitive manner. Therefore, if the phase shift Acp is to be reduced in magnitude (e.g.If the phase shift (from -90° to -45°) is to be reduced, the operating frequency must be reduced in the range -90° < Acp < 0°. Conversely, if the phase shift Acp is to be increased, the operating frequency must also be increased.

[0016] In general, an approximation method, particularly with a variable step size, can be used to approximate the operating frequency from the initial operating frequency to a lower target operating frequency at which the target phase shift is present. It is particularly advantageous that the phase shift of 0° is not reached.

[0017] In one embodiment, the specified target phase shift lies in a range of between 30° and 60°, e.g. between -60° and -30°. This is particularly advantageous for enabling particularly powerful or efficient operation of the linear compressor. This takes advantage of the fact that for maximum cooling capacity, the operating frequency is best located at the resonance frequency, which corresponds to a target phase shift of 45° associated with the resonance frequency. However, the power consumed is then also at its highest. More efficient operation for a specific cooling capacity with lower cooling capacity but even lower power or energy consumption is not at the resonance frequency, but slightly off it. It has been shown that the phase shift range for particularly efficient operation lies between 30° and 60° outside the resonance frequency.The entire target phase shift range between -60° and -30° thus encompasses the possibility of adjusting, depending on requirements, to operation at the resonant frequency for maximum cooling performance or to operation with sufficiently high cooling performance but particularly efficient operation. The desired target phase shift can be determined, for example, experimentally or through simulations.

[0018] Alternatively or additionally, the resonance frequency can be determined by the slope of the phase shift reaching a maximum, i.e., the target phase shift reaching the value d(Acp) / dt = 0 for the first time. Accordingly, for particularly efficient operation, a target phase shift with a specific slope between zero and the maximum can be specified.

[0019] One design is such that the specified target phase shift is approximately -45° or approximately 45° in magnitude. This is particularly easy to implement because it can theoretically be assumed that the resonance frequency is then met, and efficient operation of the linear compressor is achieved without any additional effort.

[0020] In one embodiment, the initial operating frequency is selected such that the corresponding phase shift is approximately 90° in magnitude. This provides the advantage that a reduction of the phase shift to a lower target value (e.g., between 30° and 60° in magnitude) can be carried out particularly reliably. In a further development, the initial operating frequency is advantageously so far removed from the target phase shift or the resonant frequency that the phase shifts for several frequency shifts are approximately -90° or approximately 90° in magnitude.

[0021] The control therefore particularly includes setting the initial operating frequency to a value significantly above the (actual or assumed) resonant frequency, and then determining the phase shift. This is typically approximately 90°. The operating frequency is then set to a new, smaller value, and the phase shift is determined again. If the phase shift does not reach or fall below the target phase shift, the operating frequency is reduced again, then the phase shift is determined, and so on. These frequency reductions are repeated until the phase shift reaches or falls below the target phase shift. The operating frequency is then set to the value whose phase shift is closest to, or has been reached, the target phase shift. For example, the range of the target phase shift can be a frequency range [f res - 3 Hz; f res+ 3 Hz], while the initial working frequency is at f res + 60 Hz. The step size Af can, for example, be Af = 1 Hz.

[0022] In one embodiment, the control system is configured to calculate a target voltage signal or a target AC voltage for the at least one drive coil of the at least one drive magnet from the currently set operating frequency and a target stroke of the lifting body. This is advantageously particularly easy to implement and enables simple implementation of a variation of the operating frequency of the lifting body. The target AC voltage can be applied as a sinusoidal voltage signal or as a pulsed, e.g., pulse-width-modulated, voltage signal.

[0023] In one embodiment, the control system is configured to calculate the phase shift for a set operating frequency from the target voltage for the linear compressor or the at least one drive coil and a measured actual current consumption of the linear compressor or the at least one drive coil. This offers the advantage of simple implementation with precise determination of the phase shift at the set operating frequency. This exploits the fact that the target voltage can be implemented very precisely, i.e. the target value and actual value differ only slightly or practically not at all. Therefore, a voltmeter for the linear compressor, in particular for its drive coil(s), can be dispensed with, and only an ammeter for the current flowing through the linear compressor, in particular its drive coil(s), is required.

[0024] One embodiment is that the control system is configured to monitor the phase shift and, if the phase shift deviates noticeably from the specified target phase shift, the operating frequency is adjusted so that the specified target phase shift is again achieved. The control system therefore recalculates the phase shift, particularly at regular intervals, and checks whether it continues to correspond to the target phase shift. If this is the case, the operating frequency is maintained. If this is not the case, the operating frequency is adjusted so that the target phase shift is again achieved.

[0025] It is an embodiment that the cooling appliance is a household appliance with a cooling device, in particular a household cooling appliance such as a refrigerator, a freezer or a combination thereof, an air conditioner, a laundry treatment appliance or a dishwasher.

[0026] The object is also achieved by a method for operating a refrigeration device equipped with a refrigeration circuit operated by a linear compressor, in which an operating frequency of a lifting body of the linear compressor, driven by at least one drive magnet equipped with at least one drive coil, is controlled such that, starting from an initial operating frequency, a phase shift between an electrical voltage applied to the linear compressor and an electrical current flowing through the linear compressor is determined, and the operating frequency is gradually reduced until a predetermined target phase shift, which is noticeably smaller than the phase shift at the initial operating frequency, is at least approximately achieved. The method can be designed analogously to the refrigeration device, and vice versa, and has the same advantages.

[0027] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an embodiment, which is explained in more detail in connection with the drawings.

[0028] Fig.1 shows a sectional side view of a sketch of a possible linear compressor;

[0029] Fig.2 shows a plot of a phase shift of a linear compressor installed in a refrigerator against the operating frequency;

[0030] Fig.3 shows a control for controlling the working frequency; and

[0031] Fig. 4 shows a sectional side view of a possible linear compressor with a driven cylinder. Fig. 1 describes a linear motor in which the piston, acting as a reciprocating body, is driven and moves relative to the cylinder as a stationary component. Fig. 4 describes a linear motor in which the cylinder, acting as a reciprocating body, is driven and moves relative to the piston as a stationary component. Figs. 2 and 3 apply to both motor variants.

[0032] Fig. 1 shows a sectional side view of a sketch of a possible linear compressor 1. The linear compressor 1 has a cylinder 2 rigidly connected to the housing 20 in a housing 20, and a piston 3 which is linearly displaceable in the cylinder 2, as indicated by the double arrow, and is provided with permanent magnets 3A. The rear side of the piston 3 is hinged to the housing 20 via a spring element 4 and the front side of the piston 3 delimits a working volume 5. A unidirectional inlet 6, through which the working medium 7 can flow into the working volume 5, and a unidirectional outlet 8, through which the working medium 7 can flow out of the working volume 5, open into the working volume 5. The linear compressor 1 also has an electromagnet or drive magnet 9 arranged outside the cylinder 2.The drive magnet 9 has a drive coil 9A, which is typically operated on the basis of an alternating voltage U~, and a stator 9B made of magnetic material, e.g. made of sheet steel segments, and then exerts a magnetic force on the permanent magnets 3A, whereby the lifting body 23 is excited to oscillate linearly in the cylinder 2. When moving forward or towards the spring element 4, the oscillating lifting body 23 elastically expands the spring element 4 and reduces the working volume 5, so that the working medium 7 is pressurized and flows out through the outlet 8 against a final pressure. Flow out through the inlet 6 is prevented, e.g. by a one-way valve. In the opposite direction towards the rear or towards the spring element 4, the lifting body 23 elastically compresses the spring element 4 and increases the working volume 5, so that a negative pressure is created there.The negative pressure, in turn, causes the working medium 7 to flow through the inlet 6 against an intake pressure. Inflow through the outlet 8 is prevented, e.g., by a one-way valve. The inlet 6 and the outlet 8 can, for example, both be arranged on a front-end valve plate 2A. The vibration system, which includes at least the lifting body 23 and the spring element 4, has a specific resonance frequency f. res At a constant alternating voltage U~, a uniform back and forth movement of the lifting body 23 occurs with a specific lifting body stroke A and a specific oscillation or working frequency f w So far, the resonance frequency f res for a specific linear compressor 1 type-related in advance (e.g. by solving a system of equations or a simulation program) and the alternating voltage U~ is directly adjusted so that the working frequency f w the type-related precalculated resonance frequency fres meets.

[0033] The control of the linear compressor shown in Fig. 1 and the linear compressor shown in Fig. 4 is explained with reference to Fig. 2 and Fig. 3. The positions x, xo and reversal points x+, ma x, x., ma x of the lifting body refer to the front of the movable piston 3 with respect to the linear compressor 1 according to Fig.1, and to the cylinder bottom 21 of the movable cylinder 2' with respect to the linear compressor T according to Fig.4.

[0034] Fig.2 shows a possible embodiment of the method according to the invention based on a schematic plot of a phase shift Acp in degrees between an applied electrical voltage and the current flow generated thereby against an associated operating frequency f w a linear compressor installed in a refrigerator 1 .

[0035] First - for example when switching on the cooling device - the working frequency f wto an initial value f w , in it is set, whose phase shift Acp is noticeably larger than a target phase shift A(p ta rget- The operating frequency f w is particularly noticeably larger than the resonance frequency f res For example, the initial operating frequency fw nit may be 100 Hz or more, while the resonance frequency f res for example, at 50 Hz. The phase shift Acp at the initial operating frequency fwjnit and, in this example, also in a wide frequency range until relatively shortly before reaching the resonance frequency f res lies on a plateau of approximately - 90°.

[0036] The working frequency f w gradually reduced (e.g. with a step size of

[0037] 1 Hz) until the corresponding phase shift Acp has dropped to the target phase shift Acptarget. The target phase shift Acptarget is a specific phase shift in a range A(p ta rget = [- 60°; - 30°], in which the phase shift A(p res = - 45°.

[0038] After the target phase shift A(p ta rget is reached, the phase shift Acp can be further monitored and the corresponding operating frequency f w in case of deviation from the target phase shift A(p ta rget should be adjusted accordingly until the target operating frequency f w , target ,where the target phase shift A(p ta rget is present, is reached again. This adjustment can be continued continuously. For a simple adjustment, the fact that the phase shift Acp in the range of the resonance frequency f reswith decreasing operating frequency f w continuously increases or decreases in magnitude. If the phase shift Acp is sign-sensitively above or below the target phase shift Acptarget, the operating frequency f w However, if the phase shift Acp is sign-sensitively below or above the target phase shift Acptarget, the operating frequency f w It is advantageous that the operating frequency f w does not enter a frequency range where the phase shift Acp reaches zero or the operating frequency f w becomes even smaller.

[0039] Fig.3 shows a control 10 for controlling the working frequency f w of the linear compressor 1, which, like the linear compressor 1, can be a component of a cooling device 11, e.g. a household refrigerator.

[0040] The control 10 is supplied with a desired piston stroke A, for example via a control device of the cooling device 11. re f is specified for the lifting body 23. The target lifting body stroke A re f is combined with a specific or desired operating frequency f w a first module ("amplitude control module") 12, which then generates the corresponding or "correct" target alternating voltage U~, re f is calculated for the drive coil 9A. The nominal AC voltage U~, re t is fed to a second module (pulse width or "PWM module") 13, which from the target alternating voltage U~, re t generates corresponding current pulses to energize the drive coil 9A. The desired alternating voltage U~, re f and the current eas measured by a current sensor 14 is fed to a third module ("phase shift calculation module") 15, which calculates the current phase shift Acp between voltage U~, re f and electricity eas calculated.

[0041] The phase shift Acp is fed to a fourth module ("frequency control algorithm") 16, which determines a specific operating frequency f w to the amplitude control module 12 and checks on the basis of the fed-back phase shift Acp whether this is on the specified target phase shift A(p ta rget or not. The frequency control algorithm 16 can then adjust the operating frequency f analogously to the processes described in Fig.2 w maintain or change it step by step. Thus, in one variant, the frequency control algorithm 16 is configured, in particular programmed, to carry out the method.

[0042] Of course, the present invention is not limited to the embodiment shown.

[0043] In general, "a", "an", etc., can be understood as a singular or a plural, in particular in the sense of "at least one" or "one or more", etc., unless this is explicitly excluded, e.g. by the expression "exactly one", etc.

[0044] A numerical value may also include the exact number stated as well as a usual tolerance range, as long as this is not explicitly excluded.

[0045] Fig. 4 shows a sectional side view of a sketch of an alternative possible linear compressor T. The linear compressor T has a cylinder 2' within a housing 20' of the linear compressor T, which cylinder, as indicated by the double arrow, is linearly displaceable relative to the piston 3', which is rigidly connected to the housing 20'. A side wall of the cylinder 2' and a cylinder base 21 act as movable walls, together with a front side of the piston 3' as an immovable wall, delimiting a working volume 5. The cylinder 2' is provided with permanent magnets 3A which are arranged on a cylinder frame 22. The cylinder frame 22 extends the cylinder 2' beyond the cylinder base 21 relative to the working volume. The cylinder 2' is hinged to the housing 20' by means of the cylinder frame 22 via a spring element 4. During operation, the cylinder 2' moves as a lifting body 23 relative to the piston 3' as a stationary component.A unidirectional inlet 6 opens into the working volume 5, through which a working medium 7 can flow into the working volume 5, and a unidirectional outlet 8, through which the working medium 7 can flow out of the working volume 5. The linear compressor 1 also has an electromagnet or drive magnet 9 arranged outside the housing 20'. The drive magnet 9 has a drive coil 9A, which is typically operated on the basis of a possibly pulsed alternating voltage U~, and a stator 9B made of magnetic material, e.g., sheet steel segments. The operated drive magnet 9 exerts a magnetic force on the permanent magnets 3A' of the cylinder 2', whereby the lifting body 23 is excited to a linear oscillating movement relative to the rigid piston 3'. With a constant alternating voltage U~, a back and forth movement of the lifting body 23 occurs at a specific oscillation or operating frequency f. wwhich at least approximately corresponds to the voltage frequency of the alternating voltage U~. In particular, the operating frequency f w a resonance frequency f res of a vibration system comprising at least the lifting body 23 and the spring element 4.

[0046] The oscillating cylinder 2' elastically expands the spring element 4 upon movement forward or toward the spring element 4 and reduces the working volume 5, so that the working medium 7 is pressurized and flows out through the outlet 8 against a final pressure. Outflow through the inlet 6 is prevented, e.g., by a one-way valve. In the opposite direction, toward the rear or toward the spring element 4, the cylinder 2' elastically compresses the spring element 4 and increases the working volume 5, creating a negative pressure there. The negative pressure, in turn, causes the working medium 7 to flow in through the inlet 6 against an intake pressure. Inflow through the outlet 8 is prevented, e.g., by a one-way valve. The inlet 6 and the outlet 8 can, for example, both be arranged on a valve plate 2A on the end face of the piston 3'. List of Reference Symbols

[0047] 1, T Linear compressor

[0048] 2, 2' cylinder

[0049] 2A valve plate

[0050] 3, 3' pistons

[0051] 3A permanent magnet

[0052] 4 spring element

[0053] 5 Working volume

[0054] 6 Entrance

[0055] 7 Working medium

[0056] 8 Outlet

[0057] 9 Drive magnet

[0058] 9A drive coil

[0059] 9B Stator

[0060] 10 Regulation

[0061] 11 Cooling device

[0062] 12 Amplitude control module

[0063] 13 PWM module

[0064] 14 Current sensor

[0065] 15 Performance calculation module

[0066] 16 Frequency control algorithm

[0067] 20, 20' housing

[0068] 21 Cylinder base

[0069] 22 cylinder frames

[0070] 23 lifting bodies

[0071] A lifting body stroke

[0072] Aref target lifting body stroke fres resonance frequency f w Working frequency fw.init Initial working frequency f w , target target operating frequency l meas Actual current U~ AC voltage

[0073] U~,ref Target AC voltage x+,max Front reversal point of the lifting body x+,max ref Front target reversal point of the lifting body x- max Rear reversal point of the lifting body xo Rest position of the lifting body

[0074] Acp phase shift

[0075] Acpres phase shift at resonance

[0076] Acptarget Target phase shift

Claims

Patent claims 1. Cooling device (11) with a refrigeration circuit operated by means of a linear compressor (1 , T) and with a control (10) which is designed to set an operating frequency (f w ) of a piston (3) or cylinder (2') driven by at least one drive magnet (9) equipped with at least one drive coil (9A) as a lifting body (23) of the linear compressor (1, T) in such a way that - starting from an initial working frequency (f w ,init) a phase shift (Acp) between an electrical voltage (U~) applied to the linear compressor (1 , T) and an electrical current (Leas) flowing through the linear compressor (1 , T) is determined and - the operating frequency (f w ) is gradually reduced until a predetermined target phase shift (Acptarget) is reached, which is noticeably smaller in magnitude than the phase shift at the initial operating frequency (f w,init) is at least approximately achieved.

2. Cooling device (11) according to claim 1, wherein the operating frequency (f w ) is reduced with a first step size until the specified target phase shift (A(pt arg et) is approximately reached, and subsequently the working frequency (f w ) with a smaller second step size until the specified target phase shift (Acptarget) is at least approximately reached.

3. Cooling device (11) according to one of the preceding claims, wherein the predetermined target phase shift (Acptarget) lies in a range between 30° and 60°.

4. Cooling device (11) according to claim 3, wherein the predetermined target phase shift (Acptarget) is approximately 45° in magnitude.

5. Cooling device (11) according to one of the preceding claims, wherein the initial operating frequency (fw nit) is selected such that the associated phase shift (Acp) is approximately 90°.

6. Cooling device (11) according to one of the preceding claims, wherein the control (10) is designed to determine from the set operating frequency (f w ) and a desired stroke (Aref) of the linear compressor (1 , T) to calculate a desired alternating voltage (U~) for the at least one drive coil (9A).

7. Cooling device (11) according to one of the preceding claims, wherein the control (10) is designed to provide a set operating frequency (f w ) to calculate the phase shift (Acp) from the target voltage (U~) and a measured actual current consumption (Leas).

8. Cooling device (11) according to one of the preceding claims, wherein the control (10) is arranged to monitor the phase shift (Acp) and, if the phase shift (Acp) deviates significantly from the predetermined target phase shift (Alptet), to adjust the operating frequency (f w ) is adjusted so that the specified target phase shift (A(pt arg et) is reached again.

9. Cooling device (11) according to one of the preceding claims, wherein the cooling device (11) is a refrigerator, a freezer or a combination thereof.

10. Cooling device (11) according to one of the preceding claims, wherein the linear compressor (1, T) has a piston (3, 3') and a cylinder (2, 2'), wherein the piston (3) is movable and drivable as a lifting body (23) relative to the cylinder (2) as an immovable component, or the cylinder (2') is movable and drivable as a lifting body (23) relative to the piston (3') as an immovable component.

11. Method for operating a cooling device (11) equipped with a refrigeration circuit operated by means of a linear compressor (1 , T), in which an operating frequency (f w ) of a lifting body (23) of the linear compressor (1 , T) driven by at least one drive magnet (9) equipped with at least one drive coil (9A) is controlled so that - starting from an initial working frequency (f w ,init) a phase shift (Acp) between an electrical voltage (U~) applied to the linear compressor (1 , T) and an electrical current (Leas) flowing through the linear compressor (1 , T) is determined and - the operating frequency (f w ) is gradually reduced until a predetermined target phase shift (Acptarget) is reached, which is noticeably smaller in magnitude than the phase shift at the initial operating frequency (f w ,init) is at least approximately achieved.

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